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Essentials of Diagnosis
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Fever, headache, altered mental status
Meningismus
Gram-positive diplococci on Gram stain of cerebrospinal fluid; counterimmunoelectrophoresis may be positive in partially treated cases
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General Considerations
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Streptococcus pneumoniae is the most common cause of bacterial meningitis in adults and the second most common cause of meningitis in children > age 6 years
Head trauma, with cerebrospinal fluid leaks, sinusitis, and pneumonia may precede it
Penicillin-resistant strains may cause meningitis
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Rapid onset, with fever, headache, meningismus, and altered mentation
Pneumonia may be present
Compared with meningitis caused by the meningococcus
Pneumococcal meningitis lacks a rash
Obtundation, focal neurologic deficits, and cranial nerve palsies are more prominent features and may lead to long-term sequelae
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Differential Diagnosis
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Meningitis due to other causes (eg, meningococcus, Listeria, aseptic)
Subarachnoid hemorrhage
Encephalitis
"Neighborhood reaction" causing abnormal cerebrospinal fluid, such as
Brain abscess
Epidural abscess
Vertebral osteomyelitis
Mastoiditis
Sinusitis
Brain tumor
Dural sinus thrombosis
Noninfectious meningeal irritation
Carcinomatous meningitis
Sarcoidosis
Systemic lupus erythematosus
Drugs (eg, nonsteroidal anti-inflammatory drugs, trimethoprim-sulfamethoxazole)
Pneumonia
Shigellosis
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See Table 30–1
Cerebrospinal fluid
Typically has > 1000 white blood cells/mcL (1 × 109/L), over 60% of which are polymorphonuclear leukocytes
Glucose concentration is < 40 mg/dL (< 2.22 mmol/L), or < 50% of the simultaneous serum concentration
Protein usually exceeds 150 mg/dL (1500 mg/L)
Gram stain shows gram-positive cocci in up to 80–90% of cases
In untreated cases, blood or cerebrospinal fluid cultures are almost always positive
Blood cultures are positive in 50% of cases
Urine antigen tests may be positive but are not sufficiently sensitive to exclude the diagnosis
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